1. Field of the Technology
The present invention relates to messages transmitting techniques, and more particularly to a method for transmitting the lower layer message of User Equipment (UE) in Multimedia Broadcast/Multicast Service (MBMS) system in a simplified way.
2. Background of the Invention
Multicast and broadcast are the techniques for transmitting data from one data source to multiple targets. In traditional mobile communication networks, Cell Multicast Service or Cell Broadcast Service (CBS) allow low speed data to be transmitted to all subscribers through cell shared broadcast channels, which belongs to message services.
Nowadays, simple telephone and message services can no longer meet requirements of subscribers on mobile communication; sharp development of the Internet has brought many new diversified mobile multimedia services. Wherein, some mobile multimedia services such as video on demand, television broadcasting, video conference, online education and interactive games etc., require that several subscribers can receive the identical data simultaneously. Compared with common data services, these mobile multimedia services have the properties of large quantity of data, long duration and are delay-sensitive. The current Internet protocol (IP) multicast and broadcast techniques can only be applied to the wired IP communication networks rather than mobile communication networks, because the mobile communication network has special network architecture, function entities and radio interfaces, which are different from those of wired communication IP network.
In order to make full use of Mobile Communication network resources, International Organization for the third Generation Standardization (3GPP) introduced the concept of multicast and broadcast (MBMS), and thereby provides Point To Multipoint (PTM) service where one data source transmits data to multiple targets in Mobile Communication networks, to share network resources and increase Utilization Ratio of network resources, and especially idle interface resources. The MBMS defined by 3GPP can not only implement multicast and broadcast of low speed messages such as plain text, but also multicast and broadcast of high speed multimedia services, which undoubtedly meets the requirements of future mobile data development.
FIG. 1 is a schematic diagram illustrating architecture of a radio network that supports Broadcast/Multicast service, as shown in FIG. 1, in prior 3GPP, entity of the radio network that supports Broadcast/Multicast service is Broadcast/Multicast service server (BM-SC) 101, and BM-SC 101 links TPF GGSN (Gateway GPRS Support Node) 102 through Gmb interface or Gi interface, one BM-SC 101 can connect with multiple TPF GGSN 102; TPF GGSN 102 further connects to SGSN (Serving GPRS Support Node) 103 via Gn/Gp interface, one GGSN 102 can connect with multiple SGSN 103; SGSN 103 can link UTRAN (Universal Terrestrial Radio Access Network) 104 of Universal Mobile Telecommunication System (UMTS) through Iu interface, and then UTRAN 104 connects with UE 106 via Uu interface, SGSN 103 can also connect with GERAN (GSM/EDGE Radio Access Network) 105 in GSM (Global System of Mobile communication) through Iu/Gb interface, and GERAN 105 further connects with UE 107 via Um interface. Wherein, both GGSN and SGSN are nodes of Core Network (CN) in radio network.
From the network structure shown in FIG. 1 it can be seen that, in order to support MBMS service, Broadcast/Multicast service center, i.e. BM-SC, the mobile network function entity was introduced into 3G Mobile Communication system, the BM-SC is the entrance to content providers, which can be used for the authorization and initiating MBMS bearer service in mobile networks and transmitting MBMS contents based on preset schedules. Besides, MBMS related functions have also been added to function entities such as UE, UTRAN, GERAN, SGSN and GGSN etc.
MBMS consists of multicast mode and broadcast mode, wherein, multicast mode requires users to subscribe in relevant Multicast group, activate the services and generate corresponding charge information. The difference between multicast mode and broadcast mode in service requirement results in dissimilar operation flow between the two modes, as shown in FIG. 2 and FIG. 3, FIG. 2 is a schematic flowchart illustrating operation in MBMS Multicast mode, while FIG. 3 is a schematic flowchart illustrating operation in MBMS Broadcast mode.
As shown in FIG. 2, processing steps involved in MBMS Multicast service includes: Subscription, Service announcement, Joining, Session Start, MBMS notification, Data transmit, Session Stop and Leaving. Wherein, the UE can subscribe wanted MBMS services in Subscription step; BM-SC may announce currently available services during Service announcement step; Joining step refers to the MBMS multicast service activating process, when the UE informs the network its willingness to be a member of current multicast group and accept multicast data of corresponding services, an MBMS UE context will be generated in the network and UE that joined the multicast group to record UE information during the joining step; in Session Start step, BM-SC will prepare data transmitting, and notify the network to establish bearer resource of relevant Core Network and access network; during MBMS notification step, the UE will be notified that MBMS multicast session will start soon; during Data transmit step, BM-SC transmits the data to the UE through bearer resource established in Session Start step, wherein, MBMS service has two modes while transmitting between UTRAN and UE: Point To Multipoint (PTM) mode and Point To Point (PTP) mode, wherein, PTM mode means that identical data will be transmitted through MTCH logical channels, and available to all UEs that subscribed Multicast service or were interested in Broadcast service, while PTP mode means data are transmitted via DTCH logical channel and available only to one corresponding UE; in Session Stop step, the bearer resource established in Session Start step will be freed; and subscribers in the group will leave the multicast group in Leaving step, which means that the UE will no longer accept Multicast data, and corresponding MBMS UE context will also be deleted in the step.
Now referring to FIG. 3, processing steps involved in MBMS Broadcast service are similar to these of MBMS Multicast service, however, it is unnecessary to implement Subscription process and Joining process before Session Start, and also unnecessary to implement leaving step after Session Stop.
During Data transmit steps of Multicast mode operation and Broadcast mode operation, MBMS service has two modes for transmitting message between UTRAN and UE: Point To Multipoint (PTM) mode and Point To Point (PTP) mode. Wherein, PTM MODE means that identical data will be transmitted through MBMS PTM service channel (MTCH), and available to all UE that subscribed Multicast service or were interested in Broadcast service; while PTP mode means data is transmitted via dedicated service channel (DTCH) and available only to one corresponding UE.
In MBMS PTM transmit mode, relevant radio control message includes service information, access information, radio bearer information and Frequency Layer Convergence (FLC) information etc., which are transmitted by Radio Resource Control (RRC) through logical channel such as MBMS PTM Control Channel (MCCH). Protocol Stack structure of MCCH is shown in FIG. 4, Protocol units of the MCCH can be listed from top to bottom as follows: RRC layer, Radio Link Control (RLC) layer, Medium Access Control (MAC) layer and Physical (PHY) layer.
In MBMS system, in order to determine optimum transport mode for each assigned MBMS service, the system introduced MBMS counting process, i.e. UTRAN employing counting process to estimate number of UEs which are interested in certain MBMS service in a cell, and the counting process differs according to different status of the UE.
According to whether RRC connection has been established in current Mobile Communication system, status of the UE can be classified into Idle mode and RRC Connected mode. Wherein, the UE that has not established RRC connection with UTRAN equipment stays in Idle mode, where, the UE can only be distinguished through identifier of Non-Access Stadium (NAS) such as International mobile subscriber identity (IMSI); and the UE that has established RRC connection with UTRAN equipment stays in RRC Connected mode, where, a Radio Network Temporary Identity (RNTI) has been assigned for the UE to act as identity of the UE in common transport channels.
Moreover, the UEs in RRC Connected mode can be further classified into different status according to different layer of RRC connection and type of transport channels available to the UE, wherein, the UE in CELL_PCH status, CELL_FACH status and CELL_DCH status can be identified on the cell layer, while the UE in URA_PCH status can be identified on UTRAN Registration Area (URA) layer. A dedicated physical channel will be assigned for the UE in CELL_DCH status, therefore, the UE can use the dedicated transport channel or shared channel or their combination; the UE in CELL_FACH status needs downlink to continuously monitor a common transport channel (FACH, Forward Access Channel.), and uplink to assign random common channel (RACH, Random Access Channel); the UE in CELL_PCH and URA_PCH status adopts Discontinuous Reception (DRX) means to monitor a Paging Channel (PCH) through relevant PICH channel, however, there are no uplink movement under these two statuses.
Generally, MBMS counting process is initiated by Radio Network Controller (RNC), when service Session Start step needs establishing radio bearer and RNC considers it is necessary, RNC issues notification message and sends probability factor simultaneously through the access information, after receiving the notification messages, the UE under Idle mode may acquire access information, and initiate RRC connection setup process to respond to counting process if probability factor check is passed; while the UE under URA_PCH status and CELL_PCH status will acquire access information after receiving the notification messages, and initiate cell update process to respond to counting process if probability factor check is passed; and the UE under CELL_FACH status will respond to counting process through other means after receiving the notification messages. Wherein, implementing probability factor check simply is to avoid collision of different UEs during accessing step and make the accessing process of UE discrete as much as possible, the method further includes following steps: generating a random number within 0˜1 and comparing the generated random number with designated probability factor, if the random number is less than the designated probability factor, then the probability factor check is passed, otherwise the probability factor checking process fails.
During counting process of the UE under Idle mode, the UE initiates the RRC connection establishment procedure through transmitting the RRC connection request message RRC CONNECTION REQUEST, when the RRC CONNECTION REQUEST message is used for the MBMS counting procedure, the RRC transmitting steps for the UE is as follows:
After contents of RRC CONNECTION REQUEST message having been configured, the UE transmitting the configured RRC CONNECTION REQUEST message on the uplink Common Control Channel (CCCH), and setting the value of the state variable V300 to 1; the RRC CONNECTION REQUEST message is transmitted via the RLC layer and MAC layer of Protocol Stack at the UE, after transmitting the message, MAC layer generating an indication to indicate whether the message had been transmitted successfully, and starting timer T318 simultaneously, and setting the value of counter N300 to 0. Wherein, V300, N300 and T318 are the variable names of the state variable, the counter and the timer regulated in standard protocol respectively.
Before timer T318 expires, if the UE has received the response message transmitted from UTRAN, then it indicates that RRC connection establishment procedure of the UE succeeds, then stopping timer T318; otherwise, waiting for the response message transmitted from the network until the timer expires. When timer T318 expires, if the value of state variable V300 is greater than that of counter N300, then the RRC connection establishment procedure of the UE fails and the UE turning into the Idle mode; besides, the UE implementing a series of operations regulated by the protocol after the UE turning from the RRC Connected mode into the Idle mode, and then finishing the entire processing procedures; otherwise, sending a new RRC CONNECTION REQUEST message on the uplink CCCH, and enabling the value of state variable V300 to increase by degrees.
From the above processing procedures, it can be seen that, the prior technical schemes have the following disadvantages: at present, no matter whether MAC layer transmitting the RRC CONNECTION REQUEST message succeeds or not, the UE initiates timer T318 in any case, however, if MAC layer informs that the RRC CONNECTION REQUEST message transmitting procedure fails, then it is unnecessary to start timer T318 any more, the counting process will be finished in this case.